Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol for fuels or consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. Hydrogenation of alkanoic acids and/or other carbonyl group-containing compounds may be carried out in the liquid phase, as described in U.S. Pat. No. 4,480,115. In the liquid phase, acetic acid is extremely corrosive and may destroy the catalysts and/or reaction equipment. U.S. Pat. No. 4,517,391 describes a cobalt catalyst for hydrogenating acetic acid in the vapor phase by feeding liquid acetic acid to the reactor. The acetic acid is vaporized in the reactor under the reaction conditions. U.S. Pat. No. 4,777,303 also reacts acetic acid in the vapor phase.
During the reduction of alkanoic acid, e.g., acetic acid, other compounds are formed with ethanol or are formed in side reactions. These byproducts and/or impurities limit the production and recovery of ethanol from such reaction mixtures. For example, during hydrogenation, esters are produced that together with ethanol and/or water form azeotropes, which are difficult to separate. In addition when conversion is incomplete, unreacted acid remains in the crude ethanol product, which must be removed to recover ethanol. The impurities may also build up in the recovery system.
Therefore, a need remains for improving vaporization of acetic acid for hydrogenation of acetic acid.